The present invention relates to maintenance of nuclear fuel assemblies comprising a skeleton formed of two end-pieces or nozzles connected by tie members fixed removably to at least the upper end-piece and grids distributed between the end-pieces and intended to hold a bundle of fuel rods confined between the end-pieces. Reference may be had to French Patent Publication No. 2,368,785 for an example of fuel assemblies of this type.
Manipulation of such an assembly presents no difficulties when it is new, but this is not the case when it has been in a reactor and so is highly radioactive. In order to avoid having to discard an assembly which has one or more defective rods after it has resided in a reactor and so is radioactive requiring manipulation from a distance under water, there have already been suggested apparatuses allowing maintenance of the assembly by replacement of one or more rods. However, the apparatuses suggested up to now, as disclosed for instance in French Patent Publication No. 2,360,963, require tilting through 180.degree. of the assembly before removing the lower end piece. This approach to the problem, based on the fact that the lower end-piece appears better adapted than the upper end-piece to removal and remounting, leads to apparatus which is extremely bulky and requires rotating of a container of very great length.
It is an object of the invention to provide apparatus allowing maintenance of a fuel assembly without requiring of the latter displacements other than horizontal and vertical rectilinear movements, while guaranteeing precise and reliable mounting in place of the components on reassembly.
For this purpose, there is provided an apparatus comprising a cell displaceable vertically in a pit where it is stored under water. The cell is provided, at its upper part, with a base plate having an opening for passage of a fuel assembly and provided with means for gripping the upper part of the fuel assembly, generally at the level of the upper grid of the latter, a guiding or centering member arranged to be manipulated by a handling tool, intended to cover the upper end-piece of the fuel assembly and to lock on to it, and means for detaching the tie members from the upper end-piece.
The invention will be better understood from the following description of apparatus which constitutes a particular embodiment, given by way of example.